Piezoelectric gauge and method of making the same



Oct 1946- M. M. SHAPIRO PIEZOELECTRIC GAUGE AND METHOD OF MAKING THE SAME Filed Feb. 10, 1944 INVENTOR. Mauriae M. Shapiro BY Q AT'IORNEY.

Patented Oct. 8, 1946 rlnzonnnc'rmo ENT-"OFFICE.

MAKING THE SAME Maurice M. Shapiro, Cabin John, Md.

Application Feb. 10, 1944, Serial No. 521,885

" 7 Claims. c1.1i,1 '327 a (Granted under. the act of March 3,1883, as

amended April 30, 1928; 370 0. G. 757) The invention relates" to improvements in piezoelectric gauges and to methods of making the same, and the primary object of the invention is to provide a piezoelectric gauge suitable for use in the observation and measurement of underwater pressure waves of large amplitude and extremely short duration, such as produced by the underwater detonation of large or small charges of high explosives. "Another object of the invention is the provision of a piezoelectric gauge having the small mass and high natural frequency which is necessary for the observation and accurate measurement of the variation of pressure with time, and themomentum associated with pressure ulses of the character described.

2 out the several views, the letter A generally designates a body of water, B an explosive charge and C the improved piezoelectric gauge.

While tests may be conducted in anyisu'it'able body'of Water, such as the open sea, in the example illustrated, the water A is containedin" an explosion test pond l0 provided'with an overhanging platform I I for supporting thee'quipment and personnel. The walls of the test pond may be provided'with irregularly curved, unevention', and a heavy water-tighttank l3 maybe A further object of the invention is to provide a. piezoelectric gauge which is rugged and permanently waterproof when exposed to the shock of underwater explosions.

The invention also aims to provide a piezoele'ctric gauge adapted for use in observing the effect of an underwater pressure wave on a submerged plate or'diaphragm having a surface exposed to the pressure wave.

The invention also is directed to'wardthe provision. of an integrally bonded and completely sealedpiezoelectric gauge and methods of making the same. 1

Other objects and advantages-of the invention will become apparent during the course of the following detailed description, taken in connection with the accompanying drawing, forming a part of this specification, and in which drawing, Figure 1 is a central vertical sectional view of an underwater explosion test pond and diagrammatically illustrating the use of the piezoelectric gauge in the observation and measurement of underwater explosion pressures.

Figure 2 is a greatly enlarged front elevational view of the gauge.

Figure 3 is a central vertical sectional view of the gauge and taken along the line 33 of Figure 2.

Figure 4 is a view partly in elevation and part ly in section illustrating a step in the method of making the gauge.

Figure 5 is a view partlyin side elevation and partly in central vertical section and showing the gauge applied to a plate having an underwater surface.

In the drawing, which for the purpose of illustration shows only a preferred embodiment of the invention, and wherein similar reference l5 exposed to the water.

embedded in one side M of the'po nd with a'wall This test pond vforms no part of the present invention and is shown merely for the purpose of illustration.

The explosive charge B may be supported in the water at any desired depth, as by a bracket [6 and a waterproof ignition cable l1.

Supported by the platform in spaced relation ,to the bracket I6 is a bracket I8 carrying the vertical leg of a depending L-shaped bar l9. At-

a bracket 2|, is a coaxial cable 22,'preferab ly of the flexible type disclosed and claimed in the copending application for patent of M. M. Shapiro and B. Stiller Serial No. 522,288 filed February 14,1944. f I

,In the example shown, the'upper end of the cable 22 is connected to suitable instruments diagrammatically indicated at 23 and the submerged end 24 is bent so as to extend forwardly and then downwardly from the horizontal leg 20. I

Referring now more particularly to Figures 2 and 3, the piezoelectric gauge C includes a thin flat hollow cylindrical housing or shell 25 formed of brass, this metal having been selected mainly because its modulus of elasticity is close to that of quartz. The'housing or, shell 25 includes a shallow pan-like container 26 comprising a fiat wall 21 and a peripheral flange 28 provided with a projectingv brass tube 29 which is silver soldered at 30 to the flange to form a water-tight joint. This tube 23 telescopes over the normally submerged'end 24 of the coaxial cable 22 and is soldered to the copper sheath 3| of the cable at 32 layers 40-43 of fusible cementitious material, l 3

such as shellac. It will be seen that the piezoelectric transducer assembly thus provided forms with the opposite end walls 21, 34 of the sheila solid body composed entirely of parallel layers which is inherently capable of withstanding extremely high pressures axially of the 'gauge. When the crystal is subjected to a changein pressure, the opposite charges developed on its two faces are transmitted by induction to electrode and the grounded cover, respectively, through the layers of shellac.

Thenontral conductor 3.1 :pf the [coaxial "ccable may be :a Nonilmor No.34-cohmr wireiinsulated with enamel and :adouble Klayer of 1 glass-fiber M4,, :and known as fiDVE or Double VitrotemEnam clad-wire. Fitted-in the inner end of the'atube 29 is a Bakelite :bushing 45 through whichrthe linsulased central :conductor fll-extends. The small space between the insulated conductor 31=and the flexible copper sheath 3| :is preferably filled with min wax 46 to prevent wibration of the conductor wdthinthenheath.

The diameter of the cylindricahshell 725-shu1d "be considerably less than the length of the presure-"wane. ,TI'IUSE-IOI underwater explosion ltests wherein the pressure-drops to one third :of its peak value in lms "than seventy microseconds, the shell preferably isless'than0ne ha1f inch in diameter and its rhiclmess should belless than one-fourth inch, :so as not :to exceed one-fourth ot-thelengthof the pressure wave.

iBefore-assemblmtm yariousparts of the gauge are prepared as follows-r The'cqpper sheath 3! 0! theloable atits end 24,-ae well-astheqinner surface of the 'brass'tube2laretinned. The edge of the cover along the rim-35 is also tinnedrto prepare it for soldering to the container flange 38. Pure orange shellac crystals are theated to the melting point; then thin coats of shellac are abpliedto thelinside'fiat surfaces of the cover 33 ,and 'oantalner 26, as well as totbothlsides of the crystal 18 and-micavsheet 33. Before .the shellac dries, the mica sheet 38 is cemented to the container wall 121 and the crystal .38 is cantrally attached to the insideof the cover wall 34.

The rimM-tonds to insure alignment of the crystalwltlrthe centerrof the cover.

In connecting the conductor 3! :to the inner sheet am r ectrode 36, the coaxial cable .22 is pushed into-the brass tube 13 beyond its normal position in the ,finishedgau'ge, .so that theineulated wire p otrudes from-thecontainer. .The Bakelite l-bushing '45 is thenslippedlover the glam iflber insulation .44, and .the bored and -.of the conductor is attached to {the electrode 36. This may be .-acoompiishod by providing-a mar- ,ginll slit in'the electrode andaoompmessing the end of the wire in the slit with .a peenahammer. Subsequently, the bushing A 'iis inserted in the tube '2! and the cable is pulled back until the electrode 36 lies iconeentrically over the mica slmet 33. Next, "the cover with thrGwCTYSifi-l at- Mohedis pressed int-,0 the :contairxer and, while pressure lsmaintain dsbymeans of a small clamp such as shown in :Figure 4, the telescopically fitting surfaces of the coverand :con-

tainer are soft-soldered together at 48. During 4 the soldering, the shellac films 40-43 melt so that upon cooling, the various parts are firmly bound together to form a solid mass. The C- clamp 41 is removed only after the metal has cooled. 4

Figure 5 illustrates means for adapting the housing or shell of the gauge C to the measurement of explosion pressures at the surface 50 of an underwater diaphragm or plate 5|. The marginal edge of this diaphragm or plate 5| may be bolted in water-tight fashion over a suitable ,openingrfllin .the exposed wall l5 of the tank l3 illustrated in Figure 1. soldered or otherwise integrally ,aifixed to the surface 5!] of the diengagement with a :thin brass nut 54 externally z'a'ffixed'atoithe container wall 21, as by silver solder 55. The diameter of the nut 54 i the same ,as that of the container, and its thickness isnot .less than thelength of'the stand -53 so that the nut may be threaded into :flrm engagement with thesurface 50.

Various changes maybe made ,in the form-oi invention andmethod =of -.manuiacture heroin :shown and described without departing irom- .the

'spirit of the {invention rori the scope oi the .following claims.

The inventiondescribed herein .may he man- 'ufactured and used by or for ,therGovernment of the United stateseof America .for-igovernmental purposes without the paymentlof any royalties thereon aortherefor.

lclaim:

1. A piezoelectric gauge iorluse intheobsenvation and measurement of -.a pressure wave of high amplitude and short duration, such ras produced by the underwater detonation-of a charge of high explosive, comprising a thinflat hollow cylindrical waterproof shell formed of elastic and elec- 'cally oonductivemetal, saidshell including spaced end-walls and a cylindrical side wallwprevided with an integral tubular -outlet, a piezoelectric transducer assembly comprising "a plurality of .thin fiat :discs :iorming with the endwalls of said cylindrical shell asoli'd :body composed entirely 'ofparallel layers and thereby inhemntly capable of withstanding extremely high pressure axially :ofthe gauge, one of :said end "walls constituting a. grounded electrode for said transducer assembly' to permit reduction in the mass and'slze of "the-gauge, the "mass of the shell being small and the greatest dimension of the shell being less than'one half inch.

2. A piezoelectric gauge for wise in observing and short duration, such as produced by the underwater detonation of a charge of high explosive, on a plate orthe like having an underwater surface, said gauge comprising a 'thin flat hollow waterproofshell formed of elastic electrically conductive metal and provided with a tubular outlet, a piezoelectric transducer assembly comprising a plurality of thin flat discs forming with the flat sides of said shell a solid body' composed entirely .of parallel layers and thereby-inherently capable of withstanding extremelyhigh pressure axially of thegauge, the mass of thegauge being negligible in comparison with the mass of said plate or the like, and screw-threaded coupling means forming a thin solid impulse-transmittim layerbet-weenone of the fiat sides of saidprgauge and said underwater surface forreleasablyfixing the gauge to said plate or the like.

3. In a piezoelectric gauge for use in the observation or measurement of a pressure wave of high amplitude and short duration, such as produced by the underwater detonation of a charge of high explosive, a thin flat hollow housing formed of elastic electrically conductive metal, said housing including a shallow pan-like container and a disc-like cover, said container comprising a fiat wall, a peripheral flange and a tubular outlet integral with said flange, said cover comprising a flat wall and an inside marginal rim telescopically fitting within said flange, a dielectric sheet adjacent one of said fiat walls, a piezoelectric crystal adjacent the other of said flat walls, a sheet metal electrode between said crystal and said dielectric sheet, a conductor extending through said outlet and connected to said electrode, and means sealing the telescopically fitting surfaces of said container and cover with said dielectric sheet, electrode and crystal in tightly clamped relation between said flat walls.

4. In a piezoelectric gauge for use in the observation or measurement of a pressure wave of high amplitude and short duration, such as produced by the underwater detonation of a charge of high explosive, a thin fiat hollow housing formed of elastic electrically conductive metal, said housing including a shallow pan-like container and a disc-like cover, said container comprising a flat wall, a peripheral flange and a tubular outlet integral with said flange, said cover comprising a flat wall and an inside marginal rim telescopically fitting within said flange, the flat wall of said cover constituting a grounded electrode, an inner sheet metal electrode disposed within the container, a dielectric sheet between said inner electrode and the flat wall of said container, a thin flat piezoelectric crystal disposed within the container between said electrodes, the periphery of said crystal being spaced inwardly of said rim, thin adhesive layers between the respective confronting surfaces of said flat walls, dielectric sheet, inner electrode and crystal, a conductor extending through said tubular outlet and connected to said inner electrode, and means sealing the telescopically fitting surfaces of said container and cover with said crystal, inner electrode, dielectric sheet and adhesive layers in tightly clamped relation between said flat walls to form an integral substantially solid laminated body.

5. In a piezoelectric gauge for use in the observation or measurement of a pressure wave of high amplitude and short duration, such as produced by the underweater detonation of a charge of high explosive, a thin flat hollow housing formed of elastic electrically conductive metal, said housing including a shallow pan-like container and a disc-like cover, said container com prising a flat Wall, a peripheral flange and a tubular outlet integral with said flange, said cover comprising a flat wall and an inside marginal rim telescopically fitting within said flange, the flat wall of said cover constituting a grounded electrode, an inner sheet metal electrode disposed within the container, a dielectric sheet between said inner electrode and the fiat wall of said container, a thin fiat piezoelectric crystal disposed within the container between said electrodes, the peripheries of said crystal and said inner electrode being spaced inwardly of said rim and flange respectively, thin layers of a fusible adhesive between the respective confronting surfaces of said flat walls, dielectric sheet, inner electrode and crystal, a conductor extending through said tubular outlet and connected to said inner electrode, and a solder joint sealing the telescopically fitting surfaces of said container and cover against the ingress of water or moisture, with said crystal, inner electrode, dielectric sheet and adhesive layers in tightly clamped and adhesively bonded relation between said flat walls.

6. In a piezoelectric gauge for use in the observation or measurement of a pressure wave of high amplitude and short duration, such as produced by the underwater detonation of a charge of high explosive, a thin flat hollow water-tight shell formed of elastic electrically conductive metal, said shell including parallel sidewalls and a peripheral wall and being provided with a tubular outlet integral with said peripheral wall, one of said parallel sidewalls constituting a grounded electrode, an inner sheet metal electrode disposed within the shell, a dielectric sheet between said inner electrode and the other of said parallel sidewalls, a thin flat piezoelectric crystal disposed within the shell between said electrodes, the peripheries of said crystal and said inner electrode being spaced inwardly of the peripheral wall of the shell, thin adhesive layers bondin t respective confronting surfaces of said parallel sidewalls, dielectric sheet, inner electrode and crystal so as to form an integral laminated body substantially devoid of pockets between said respective confronting surfaces, a conductor extending through said tubular outlet and connected to said inner electrode, and means for insulating said conductor therefrom.

7. The method of assembling a piezoelectric gauge including a metal container, a plurality of .thin flat elements fitting in the container and a telescopically fitting metal cover, to form an integral waterproof unit, said method comprising applying a fusible cement coating to at least one of each pair of confronting surfaces of said elements, container and cover to hold said elements in a predetermined preliminarily assembled relationship, disposing said cover in telescopically fitted relation to the container with said preliminarily assembled elements in the container, pressing said cover and container together so as to tightly hold said elements in predetermined position therebetween, soldering the telescopically fitting surfaces of said container and cover with said fusibly cemented elements clamped therebe tween so as to remain in predetermined relationship upon fusing of said coatings as a result of the soldering operation, and cooling said container to a temperature below the fusing temperature of said cement before removing the pressure on the container and cover.

MAURICE M. SHAPIRO. 

